Linearity improvement in amplifiers by using gm3 cancellation is a widely used technique in power amplifiers and low noise amplifiers as described by Kim, J. H., Cho, C. S., Lee, J. W., and Kim, J. in “Linearity Improvement of Class-E Doherty Amplifier Using gm3 Cancellation” Electronics Letters Volume: 44, Issue: 5, and by Rajashekharaiah, M., Upadhyaya, P., and Deukhyoun Heo in “Enhance gm3 Cancellation or Linearity Improvement in CMOS LNA” IMS2006.
The gm3 cancellation method is one method used to remove third-order intermodulation distortion (IMD3). However, gm3 cancellation happens only within a narrow bandwidth, because it is hard to cancel the exact amplitude and phase of two third harmonics across a broad bandwidth.
Also in the prior art, many broadband amplifiers are realized based on distributed amplifier architectures; however, such architectures are known to be proper only for achieving broadband gain, because linearity is generally neglected or sacrificed to obtain the broadband gain.
A gm3 cancellation circuit for a CMOS based distributed amplifier is described by El-Khatib, Z., MacEachern, L., and Mahmoud, S. A. in “CMOS Interleaved Distributed 2×3 Matrix Amplifier Employing Active Post Distortion and Optimum Gate Bias Linearization Technique” Electrical and Computer Engineering 2010; however, the distributed amplifier paired two transistors as one cell, which is difficult to adapt to a compound based semiconductor process, because only one threshold voltage is available. Also, as described, a huge capacitor is needed on every unit cell to separate each device gate bias, which makes a circuit layout very messy and makes routing transmission lines with the proper length difficult.
What is needed are power amplifiers and amplifiers for LNAs that have broadband linearity. The embodiments of the present disclosure answer these and other needs.